The invention relates to an extrafine copper alloy wire, an ultrafine copper alloy wire, and a process for producing the same, and more particularly to an extrafine copper alloy wire, with an outer diameter of 0.02 to 0.1 mm, possessing excellent bending fatigue lifetime and torsional strength and an ultrafine copper alloy wire, with a wire diameter of not more than 0.08 mm, possessing excellent tensile strength, electrical conductivity, and drawability and good elongation, and a process for producing the same.
A reduction in size of electronic equipment, IC testers, medical ultrasound system and the like has led to an ever-increasing demand for a reduction in diameter of electric wires for use in these types of equipment. In general, conductor wires for electric wires used in this field are classified into three groups, that is, products having an outer diameter of more than 0.1 mm, products having an outer diameter of 0.02 to 0.1 mm, and products having an outer diameter of less than 0.02 mm.
For conductor wires having an outer diameter exceeding 0.1 mm, importance is attached to torsional properties and elongation from the viewpoint of preventing loosening of wires, for example, during twisting work or working of terminals. In general, for this application, annealed tough pitch copper (TPC), which is advantageous from the viewpoints of low price and good electrical conductivity, has been used.
For conductor wires having an outer diameter of less than 0.02 mm, wires are highly likely to be broken during extrusion of an insulator due to the very small diameter. For this reason, a copper-tin alloy is used which possesses excellent tensile strength and flexing resistance although the copper-tin alloy has somewhat low electrical conductivity.
For extrafine conductor wires having an intermediate size, that is, an outer diameter of 0.02 to 0.1 mm, annealed TPC is used when twistability, workability of terminals, and high electrical conductivity are required, while wire drawn product of copper-tin alloys are used when flexing resistance is required.
According to the conventional extrafine conductor wires having an intermediate size, however, the strength of the annealed TPC is so low that the bending fatigue lifetime is unsatisfactory, while, when the wire drawn products of copper-tin alloys are used, the elongation and torsional strength are so low that there is a high fear of wires being loosened, for example, during twisting work or working of terminals of electric wires.
In the case of electric wires for medical ultrasound system, there is a demand for electric wires (cables) which have an increased number of wire cores (micro coaxial cables) while maintaining the outer diameter of conventional electric wires.
To this end, high strength, high flexing resistance, high electrical conductivity, good twistability, and good workability of terminals are required of conductors for electric wires. In this case, importance is attached to high strength, flexing resistance, and high electrical conductivity among these property requirements, and, at the present time, electric wires using a hard material of a dilute copper alloy as the conductor constitute the mainstream of electric wires for medical ultrasound system.
This electric wire for medical ultrasound system comprises a large number of ultrafine copper alloy wires stranded together. The ultrafine copper alloy wire is produced by melting a dilute copper alloy, casting the molten alloy into a wire rod, and then drawing the wire rod through a die to a diameter of 0.03 mmxcfx86.
When an ultrafine copper alloy wire having a smaller diameter (for example, not more than 0.025 mmxcfx86) is used as a conductor for electric wires from the viewpoint of further reducing the diameter of electric wires for medical ultrasound system, however, excessively low breaking strength of the conductors using the conventional copper alloy causes frequent wire breaks at the time of wire drawing or stranding of the conductors. For this reason, the formation of ultrafine copper alloy wires having a diameter of not more than 0.025 mmxcfx86 using conventional alloys was very difficult.
Thus, ultrafine copper alloy wires having higher tensile strength have been desired. Merely increasing the tensile strength, however, results in lowered electrical conductivity. This has led to a demand for copper alloys having both high tensile strength and high electrical conductivity.
Further, excellent drawability is required for the formation of ultrafine copper alloy wires having a diameter of not more than 0.025 mmxcfx86. When a wire rod is drawn by dicing, the presence of foreign materials having a size of about one-third of the wire diameter in the wire rod poses a problem of wire breaks. Therefore, the amount of foreign materials contained in the wire rod should be reduced to improve the wire drawability.
Detailed analysis of the foreign materials contained in a sample of a broken wire has revealed that the cause of the inclusion of foreign materials in the wire rod is classified roughly into two routes. One of them is inclusions contained in the copper alloy as a base material and the metallic elements as the additive, and peeled pieces produced by the separation of refractories such as SiC, SiO2, and ZrO2, which are components of ceramics and cement used in crucibles employed in melting and/or molds used in casting. The other route is foreign materials externally included during wire drawing. Among these foreign materials, the inclusion of the latter type of foreign materials can be reduced by performing the step of wire drawing in a clean environment.
On the other hand, improving the quality of the base material (improving the purity of substances constituting the base material) is necessary for reducing the amount of the former type of foreign materials (inclusions and peeled pieces). Therefore, when ultrafine wires are formed by wire drawing, very careful attention should be paid so as to avoid the inclusion of foreign materials in steps from melting to wire drawing, and the factor in the inclusion of the foreign material should be minimized.
Further, in the case of ultrafine copper alloy wires having a diameter of not more than 0.025 mmxcfx86, the twistability and the workability of terminals, that is, elongation, in addition to the tensile strength and the electrical conductivity, become important.
The invention has been made with a view to solving the above problems of the prior art, and it is an object of the invention to provide an extrafine copper alloy wire, with an outer diameter of 0.02 to 0.1 mm, possessing excellent bending fatigue lifetime based on high tensile strength and excellent torsional strength based on high elongation, and a process for producing the extrafine copper alloy wire.
It is another object of the invention to provide an ultrafine copper alloy wire possessing excellent tensile strength, electrical conductivity, and drawability and, at the same time, good elongation, and a process for producing the ultrafine copper alloy wire.
The features of the invention will be summarized below.
(1) An extrafine copper alloy wire comprising
a copper alloy wire having an outer diameter of 0.02 to 0.1 mm,
said copper alloy wire being formed of a heat treated copper alloy comprising 0.1 to 0.9% by weight of tin and not more than 50 ppm of oxygen with the balance consisting of copper.
In this feature of the invention, the content of tin is limited to 0.1 to 0.9% by weight. When the tin content is less than 0.1% by weight, the strength is unsatisfactory and, in its turn, the bending fatigue lifetime is unsatisfactory. On the other hand, when the tin content exceeds 0.9% by weight, the elongation is unsatisfactory. This results in lowered torsional strength and, thus, causes a problem of loosening of wires at the time of stranding or working of terminals in electric wires.
The content of oxygen is limited to not more than 50 ppm. When the oxygen content exceeds 50 ppm, an oxide of tin is produced and, thus, the amount of the tin component dissolved in copper to form a solid solution is unsatisfactory.
(2) The extrafine copper alloy wire according to item (1), wherein said copper alloy wire has a bending fatigue lifetime of not less than 4,000 times as measured by repeatedly flexing a sample of the copper alloy wire in the right direction at an angle of 90xc2x0 and in the left direction at an angle of 90xc2x0 and a flexing strain of 0.8% while applying a load corresponding to 20% of the breaking load, and a torsional strength of not less than 250 times as measured by stranding a sample of the copper alloy wire while applying a load corresponding to 1% of the breaking load.
(3) An extrafine copper alloy wire comprising
a copper alloy wire having an outer diameter of 0.02 to 0.1 mm,
said copper alloy wire being formed of a heat treated copper alloy comprising 0.1 to 0.9% by weight of tin, 0.1 to 0.5% by weight of indium, and not more than 50 ppm of oxygen with the balance consisting of copper.
(4) The extrafine copper alloy wire according to item (3), wherein said copper alloy wire has a bending fatigue lifetime of not less than 4,000 times as measured by repeatedly flexing a sample of the copper alloy wire in the right direction at an angle of 90xc2x0 and in the left direction at an angle of 90xc2x0 and a flexing strain of 0.8% while applying a load corresponding to 20% of the breaking load, and a torsional strength of not less than 250 times as measured by stranding a sample of the copper alloy wire while applying a load corresponding to 1% of the breaking load.
Indium has the effect of further improving the bending fatigue lifetime and the torsional strength. In order to attain this effect, the indium content should be at least 0.1% by weight. On the other hand, the upper limit of the indium content should be 0.5% by weight. The addition of indium in an amount exceeding 0.5% by weight should be avoided because the elongation and the torsional strength are deteriorated although the strength and the bending fatigue lifetime are increased.
The presence of unavoidably included impurities besides the above-described tin, oxygen, and indium poses no problem, and other constituents may be added so far as they are not detrimental to the object of the invention.
(5) A process for producing an extrafine copper alloy wire, comprising the steps of:
drawing a copper alloy to produce a wire having an outer diameter of 0.02 to 0.1 mm, the copper alloy comprising 0.1 to 0.9% by weight of tin and not more than 50 ppm of oxygen with the balance consisting of copper; and
then heat treating the wire at 500 to 800xc2x0 C.
In this production process, the heat treatment temperature is limited to 500 to 800xc2x0 C. When the heat treatment temperature is below 500xc2x0 C., a lot of time is required for the heat treatment. Therefore, the cost is increased, and, thus, the profitability is lost. On the other hand, when the heat treatment temperature is above 800xc2x0 C., the resultant extrafine copper wire is soft and thus is likely to be broken during working of wires in the production of electric wires.
(6) The process according to item (5), wherein the heat treatment is carried out by traveling the wire through a tubular furnace heated at a predetermined temperature.
Preferably, the heat treatment is carried out by continuously traveling the wire through a tubular heating furnace. Unlike the conventional heat treatment method wherein the wire is wound around a bobbin and, in this state, heat treated, according to this method, for example, seizing or adhesion between wires does not occur, and, in addition, heat can be homogeneously applied to the wires, thus realizing the production of homogeneous extrafine copper wires. The inside of the tubular heating furnace is preferably filled with inert gas such as nitrogen or argon gas.
(7) A process for producing an extrafine copper alloy wire, comprising the steps of:
drawing a copper alloy to produce a wire having an outer diameter of 0.02 to 0.1 mm, the copper alloy comprising 0.1 to 0.9% by weight of tin, 0.1 to 0.5% by weight of indium, and not more than 50 ppm of oxygen with the balance consisting of copper; and
then heat treating the wire at 500 to 800xc2x0 C.
(8) The process according to item (7), wherein the heat treatment is carried out by traveling the wire through a tubular heating furnace heated at a predetermined temperature.
The extrafine copper alloy wires according to the invention have the following properties.
Specifically, the extrafine copper alloy wires according to the invention are characterized by having a bending fatigue lifetime of not less than 4,000 times as measured by repeatedly flexing a vertically suspended sample of the extrafine copper alloy wire in the right direction at an angle of 90xc2x0 and in the left direction at an angle of 90xc2x0 and a flexing strain of 0.8% while applying a load corresponding to 20% of the breaking load of the copper alloy wire to the sample, and having a torsional strength of not less than 250 times in terms of the number of times of torsion required for causing wire breaks as measured by stranding the upper end of a sample of the extrafine copper alloy wire in one direction while applying a load corresponding to 1% of the breaking load of the copper alloy wire to the lower end of the sample.
The bending fatigue lifetime of not less than 4,000 times is a precondition for a guarantee for the flexing properties of this type of extrafine copper alloy wires having an outer diameter of 0.02 to 0.1 mm. On the other hand, the torsional strength of not less than 250 times in terms of the number of times of torsion is also important for preventing wires from loosening, for example, during stranding or working of terminals of electric wires.
Further, the extrafine copper alloy wires according to the invention are characterized by having a tensile strength of not less than 40 kgf/mm2, an elongation of not less than 8%, and an electrical conductivity of not less than 70% IACS.
When the tensile strength is less than 40 kgf/mm2, it is difficult to ensure the bending fatigue lifetime of not less than 4,000 times. When the elongation is less than 8%, it is difficult to ensure the torsional strength of not less than 250 times. When the electrical conductivity is less than 70% IACS, the electrical loss is unfavorably increased in signal wire applications.
(9) An ultrafine copper alloy wire formed of an alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 1 ppm and, contained in the matrix, 0.05 to 0.9% by weight of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron, said wire having been drawn to a final diameter of not more than 0.08 mm and annealed.
The total content of the unavoidable impurities in the high purity copper is limited to not more than 1 ppm from the viewpoint of minimizing the content of inclusions in the copper matrix. More specifically, a major part of the unavoidable impurities is accounted for by oxygen (O), and this oxygen combines with copper contained in the copper matrix to form a compound (Cu2O) which becomes inclusions having a particle diameter of about 2 xcexcmm. In general, the particle diameter of inclusions causative of wire breaks is said to be not less than about one-third of the wire diameter. There is a possibility that even inclusions having a smaller particle diameter cause wire breaks. For this reason, the total content of the unavoidable impurities in the high purity copper is limited to not more than 1 ppm.
The amount of the metallic element contained in the copper matrix in the high purity copper is limited to 0.05 to 0.9% by weight. When the amount of the metallic element contained in the copper matrix is less than 0.05% by weight, a tensile strength of 300 to 500 MPa cannot be ensured. On the other hand, the amount of the metallic element is larger than 0.9% by weight, an electrical conductivity of not less than 70% IACS cannot be ensured.
(10) An ultrafine copper alloy wire comprising:
a core wire formed of an alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 1 ppm and, contained in the matrix, 0.05 to 0.9% by weight of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron, said wire having been drawn to a final diameter of not more than 0.08 mm and annealed; and,
provided on the periphery of the core wire, a tin plating, a silver plating, a nickel plating, a tin-lead solder plating, a tin-copper-bismuth-base lead-free solder plating, or a tin-silver-copper-base lead-free solder plating.
The diameter of the ultrafine copper alloy wire after drawing is limited to not more than 0.08 mm. When the wire diameter is larger than 0.08 mm, even conventional materials can stably provide extrafine copper alloy wires.
(11) A process for producing an ultrafine copper alloy wire, comprising the steps of:
performing melting and casting respectively using a carbon crucible and a carbon mold to form a wire rod formed of an alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 1 ppm and, contained in the matrix, 0.05 to 0.9% by weight of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron;
drawing the wire rod to form a wire having a final diameter of not more than 0.08 mm; and
then annealing the wire.
The material constituting the crucible and the mold should be a carbon, from the viewpoint of avoiding the inclusion of pieces peeled from the crucible and the mold in the molten metal and the cast material during melting and casting.
The reason why the annealing treatment is carried out while traveling the wire is that, when a wire wound around an iron bobbin is placed in a furnace to perform annealing, there is a fear of causing adhesion between wires, leading to a problem of quality.
(12) The process according to item (11), wherein the annealing of the wire is carried out by traveling the drawn wire through a tubular furnace having an atmosphere of reducing gas including a mixed gas composed of argon gas and hydrogen gas.
(13) The process according to item (11), wherein the annealing of the wire is carried out by electric heating.
(14) The process according to item (11), which further comprises the step of forming a tin plating, a silver plating, a nickel plating, a tin-lead solder plating, a tin-copper-bismuth-base lead-free solder plating, or a tin-silver-copper-base lead-free solder plating on the periphery of the annealed wire as the core wire.
(15) An electric wire comprising a plurality of ultrafine copper alloy wires stranded together, said ultrafine copper alloy wires each being formed of an alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 1 ppm and, contained in the matrix, 0.05 to 0.9% by weight of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron, said wire having been drawn to a final diameter of not more than 0.08 mm and annealed.
(16) An electric wire comprising a plurality of ultrafine copper alloy wires stranded together, said ultrafine copper alloy wires each comprising: a core wire formed of an alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 1 ppm and, contained in the matrix, 0.05 to 0.9% by weight of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron, said wire having been drawn to a final diameter of not more than 0.08 mm and annealed; and, provided on the periphery of the core wire, a tin plating, a silver plating, a nickel plating, a tin-lead solder plating, a tin-copper-bismuth-base lead-free solder plating, or a tin-silver-copper-base lead-free solder plating.
(17) An extrafine copper alloy wire comprising
a copper alloy wire having an outer diameter of not more than 0.1 mm,
said copper alloy wire being formed of a heat treated copper alloy comprising 0.05 to 0.9% by weight in total of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron and not more than 50 ppm of oxygen with the balance consisting of copper.
(18) A micro coaxial cable comprising:
an inner conductor comprising a plurality of extrafine or ultrafine copper alloy wires, according to item (1), (3), (9), (10), or (17), stranded together;
an insulation covering the inner conductor;
an outer conductor comprising a plurality of extrafine or ultrafine copper alloy wires spirally wound on the insulation at predetermined pitches; and
a jacket as the outermost layer of the micro coaxial cable.
(19) The micro coaxial cable according to item (18), wherein the extrafine or ultrafine copper alloy wire constituting the outer conductor is one according to item (1), (3), (9), (10), or (17).